SAN DIEGO -- Two girls who attend a Carmel Valley elementary school have been sickened with E.coli infection, the San Diego County Health and Human Services Agency reported Wednesday.

The girls, ages 7 and 9, have been hospitalized and are expected to recover, according to the HHSA.

Health officials have not determined the source of the E.coli, but officials at Carmel Creek Elementary have notified parents as a precaution, according to the HHSA.

"The school has not been named as the source, but we appreciate their cooperation during this investigation," said Dr. Wilma Wooten, the county's public health officer.

"We emphasize to the public that it is critical to practice appropriate food safety habits and good hand hygiene to prevent infectious diseases like E.coli from spreading," she said.

E.coli can come from a number of sources, including lettuce, raw milk, unpasteurized apple cider, undercooked hamburger or from petting zoos and animal exhibits, county health officials said.

E.coli infection often causes abdominal cramps and bloody diarrhea. There is usually little or no fever, and the illness typically resolves itself in five to 10 days. But a small percentage of those infected may develop a condition in which red blood cells are destroyed and kidney failure may occur.

Those most at risk for food-borne illnesses include young children, the elderly and those with compromised immune systems.